1. Field of the Invention
The present invention relates to the treatment of nitrogenous gaseous effluents produced during various organic syntheses comprising a nitric oxidation phase to decease the nitrous oxide content thereof, prior to the release of same into the atmosphere.
2. Description of the Prior Art
Certain organic compound syntheses include the nitric acid oxidation of an intermediary. Thus, for example, adipic acid is produced via nitric oxidation of cyclohexanol, glyoxal via nitric oxidation of acetaldehyde, and glyoxylic acid via nitric oxidation of glyoxal. Nitrous oxide, N.sub.2 O, is an abundant, undesirable byproduct of these reactions.
These gaseous effluents also contain, in addition to the very large proportion of nitrous oxide, nitrogen, oxygen, carbon dioxide, and nitrogen oxides, such as NO and NO.sub.2. The composition of such gases is typically as follows:
N.sub.2 O: 30-50% PA0 CO.sub.2 : approximately 5% PA0 O.sub.2 : 1-4% PA0 NO.sub.x : 0-5,000 ppm PA0 N.sub.2 : complementary amount.
To date, procedures for the purification of such effluents have been limited to removing the NO.sub.x by washing with water in an absorption tower. The gases were then released or vented into the atmosphere without further treatment. This situation has become unacceptable for environmental protection reasons.
The catalytic decomposition of N.sub.2 O using a silver-based catalyst supported on aluminum oxide, whether doped or undoped, is known to this art (DE-4,128,629). In reality, this process operates effectively only if the gas/catalyst contact times are sufficiently lengthy (illustrated by relatively low hourly volumetric velocities, i.e., of approximately 4,000 h.sup.-1). As regards the highest hourly volumetric velocities normally encountered in industry, these aluminum oxide based catalysts are less effective.
The completely different field of nitric acid production via ammonia oxidation also presents the problem of treatment prior to atmospheric release of gaseous effluents containing various nitrogen oxides, the NO.sub.x content of which is sought to be removed before release into the atmosphere. Published French patent applications Nos. 2,613,253 and 2,622,474 describe techniques for destroying NO.sub.x using ammonia and catalyzed by mordenites. Under these conditions, it has been determined that the outlet gases contain virtually as much nitrous oxide as before treatment. These industrial scale results are in apparent contradiction with scientific literature reporting catalysis of the decomposition of nitrous oxide on similar aluminosilicates (in particular, Aparicio et al as regards the catalytic activity of Y zeolites or exchanged mordenites (J. Catal., Vol. 104(a), p. 381; Vol. 108(1), p. 233; Vol. 110(2), p. 330).